GB2455569A - An electromagnetic actuator remotely controlled and powered via a telephone line - Google Patents

Abstract

A remotely controlled electro-mechanical actuator, or a method of its operation, comprises charging a capacitor 17 from a power supply with a maximum supply current which is less than that required to drive the actuator 11. A public switched telephone network (PSTN) telephone line is used to provide the power and control signals. The capacitor 17 may have a capacitance of more than 1F or more than 5F with a leakage current of less than 50žA. A control signal may be used to switch between trickle charge and recharge modes to the capacitor 17. The actuator 11 may drive a hydraulic valve arrangement. The actuator 11 has a linear movement mechanism. This mechanism may include means of converting the rotary movement of a stepping motor into a liner movement. The telephone line input has a maximum power line supply current less than the required drive current of the linear actuator 11, and a leakage current of the capacitor 17 is less than the maximum allowed telephone line on-hook supply current.

Description

ELECTRO-MECHANICAL ACTUATOR

This invention relates to electro-mechanical actuators, and particularly to remotely controlled actuators.

There are many examples of electro-mechanical actuator where it is desirable to have the ability to control the device remotely. One example is water valves, which are used to isolate sections of the water mains supply system, to allow repairs or replacement to be carried out. In the event of a failure or damage to a water mains pipe, it is desirable to isolate the fault as quickly as possible. Of course, the water supply system extends to many remote areas, and it has been recognised that the ability to control the gate valves remotely is desirable.

It is known to provide telephone-based control commands to remote devices, using a telephone modem to interpret control commands. The use of the internet and/or mobile phones for controlling remote devices is also now widespread, and this has the advantage that control signals can be provided wirelessly.

A problem with the remote control of electrical devices is that a power supply is nevertheless needed to drive the device. For devices in remote applications, where remote control is particularly desirable, there is often no mains electrical supply.

According to the invention, there is provided a remotely controlled electro-mechanical actuator, comprising: a linear actuator for providing mechanical actuation; a capacitor for storing charge for use in driving the linear actuator; a power line input; and a control circuit for controlling the operation of the linear actuator using a control signal received from a remote location, wherein the power line input is for connection to a power source with a maximum power line supply current less than the required drive current of the linear actuator, and a leakage current of the capacitor is less than the maximum power line supply current.

This use of a capacitor with a low leakage current (e.g. below 5OpA) enables the leakage current to be supplied by a phone line, so that the on-hook allowed current draw from the phone line can be used to charge the capacitor and maintain the capacitor charged. Thus, the power line input can be connected to a Public Switched Telephone Network (PSTN) or telephone line.

A high capacitance is preferred, for example of more than iF, and this enables the capacitor to provide the required short term current surge to operate the linear actuator. Preferably, the desired duty cycle with which the linear 10' actuator is driven is very low. For example, the operation of the device can be completed in the order of a second or seconds, whereas the time between successive operations will typically be at least minutes.

The high desired capacitance can be obtained using a capacitor which comprises activated carbon electrodes, and an electrode separator soaked in electrolyte. The capacitor preferably has a leakage current of less than 2OpA. This is well below the allowed 5OpA on-hook current draw for phone lines in some countries. The capacitor may have a very large capacitance of more than 5F.

The actuator may further comprise a phone line input for connection to a phone line power supply for providing a trickle capacitor charge current. This means that mains power is not required to power the device, Instead, the phone line is used to draw a trickle current to keep the capacitor charged, and the capacitor provides the short period high current pulse to operate the linear actuator.

The control circuit can control the charge flow to the capacitor from the phone line input. This enables the system to operate without exceeding the allowed phone line currents.

The control circuit can be operable in two modes: a first, trickle charge mode, in which a current of less than a maximum phone line on-hook permissible current (e.g. 5OpA in the UK)' is provided both to keep electronic control circuit in a "waiting mode" ready to accept control signal from PSTN and compensate a leakage current of the capacitor; and a second, recharge mode, in which a current of less than a maximum phone line off-hook current (e.g. lOOmA) is provided from the phone line input to charge the capacitor.

The recharge mode is initiated during an active call. This active call is then used to aHow a larger current to be used to charge the capacitor more quickly, if required. The call also enables the required control commands to be provided to the control circuit in a double-tone multifrequency mode (DTMF).

The linear actuator can control a valve, for example a pilot/control valve of a hydraulic valve.

The invention also provides a hydraulic valve, comprising: a valve disc provided in the fluid path between a fluid inlet and outlet; a valve disc control chamber, wherein the pressure in the valve lever control chamber controls the open or closed position of the valve; a first fluid connection between the fluid inlet and the control chamber; and an actuator of the present invention for selectively coupling the control chamber to the first fluid connection.

In this invention, the linear actuator can also control a pressure regulator which can be connected in a pressure regulating loop of a known hydraulic pressure control valve, for example for pressure reduction.

The invention also provides a method of remotely controlling an electro-mechanical actuator, comprising: supplying power to the actuator from a telephone line having a maximum power supply current less than the required drive current of the actuator; charging a capacitor using the telephone line power supply; providing a control signal over the telephone line; operating the actuator using charge stored in the capacitor in response to the control signal; and recharging the capacitor using the telephone line power supply.

An example of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a known hydraulic control valve; Figure 2 shows schematically the electrical layout of an actuator of the invention; Figure 3 shows schematically the mechanical layout of a 3-way pilotlcontrol valve, driven by a linear actuator, which can be used as the control valve in the valve of Figure 1; and Figure 4 shows an alternative use of the actuator of the invention.

The invention provides a remotely controlled electro-mechanical actuator, in which a capacitor stores charge for use in driving a linear actuator for providing mechanical actuation for driving an external device. The power line input is for connection to a power source with a maximum power line supply current less than the required drive current of the linear actuator, and a leakage current of the capacitor is less than the maximum power line supply current.

In a preferred arrangement, the actuator comprises a telephone line interface and communication controller, a power and liner actuator controller and a linear actuator The actuator can thus be powered by a phone line, as result of a large capacitance of the implemented capacitor with a low leakage current.

One application of particular interest is for the remote control of water control valves, for example used in the mains water system. For this reason, the operation of a typical hydraulic control valve used in that application will first be described with reference to Figure 1.

The hydraulic valve comprises a fluid inlet 1 and a fluid outlet 2. A valve seal disc 3 is provided in the fluid path between the fluid inlet and the fluid outlet and can close the fluid inlet as shown in Figure 1. A valve seal disc control chamber 4 is used to control the open or closed position of the valve seal disc 3.

The pressure in the chamber 4 acts against a diaphragm 5 which is connected to the valve seal disc 3 by a rod 6. When the pressure in the control chamber 4 is equal to the inlet pressure, the valve is closed, as a result of differential areas, i.e. the control chamber pressure acts on a larger area than the area of the seal disc exposed to the inlet fluid flow. Thus, the valve can be closed by providing a fluid connection between the chamber 4 and the inlet 1, for example as shown by connecting pipes 7 and 8.

To open the valve, the pressure in the chamber 4 is reduced. This can be by venting the chamber to air, or by connecting it to a different area with a low pressure, for example the outlet side of the valve by pipes 8 and 9.

A small pilot/control valve 10 can be used for controlling the overall valve operation by controlling the coupling of the pipe 8 to pipe 7 or 9.. This control valve is not exposed to the fluid flow rates or volumes of the main valve and can therefore be a reliable low cost device. It can be mechanically operated and/or electrically operated.

This invention relates to remotely controlled actuators, such as low current valves to perform the pilot/control valve function.

Figure 2 shows schematically the electrical layout of an actuator of the invention, which can be used as the control valve 10 in the hydraulic valve of Figure 1. Figure 3 shows the mechanical layout. As shown, the arrangement has three inputs/outputs, with a valve lever in the path between two of the inputs/outputs, to selectively block one of them.

The actuator of the invention comprises a linear actuator 11 for providing mechanical actuation. This provides the desired mechanical movement to operate the pilot/control valve 10. The linear actuator provides linear reciprocation of an output shaft, and this can be used to move a closing lever of the valve between two positions. This is shown schematically in Figure 3, in which the reciprocating shaft is shown as 12, and which drives a valve seal lever 13 between two positions, to selectively close one of two passages 14 or 15. In this way, an inlet passage 16 is selectively coupled to one or other of the passages 14 or 15. In this example, the inlet passage 16 can be connected to the control chamber 4, and the other passages 14 and 15 can be connected to the inlet 1 and outlet 2 of the hydraulic valve, Fig.1.

A capacitor(s) 17 (Fig.2) stores charge for use in driving the linear actuator 11 and typically has a leakage current of less than 5OpA and a capacitance of more than iF.

This use of a capacitor with a leakage current below 5OpA enables the leakage current to be supplied by a phone line 19, so that the on-hook allowed current draw from the phone line can be used to charge the capacitor and maintain the capacitor charged. The high capacitance of more than iF enables the capacitor to provide the required short term current surge to operate the linear actuator. Preferably, the desired duty cycle with which the linear actuator is driven is very low. For example, the operation of the device can be completed in the order of a second or seconds, whereas the time between successive operations will typically be at least minutes.

A preferred example of linear actuator is a hybrid linear actuator that converts the rotary motion of a stepping motor into linear motion by the most effective way -within the stepper motor itself. This type of linear actuator features precision, reliability and unmatched performance-to-size ratios, for example from the company Haydon Switch and Instruments, Inc. The most important features of a hybrid linear actuator is its very high thrust and ability to maintain the same position of its shaft after de-energising of the actuator withstanding considerable forces that can be applied to the shaft.

Known hybrid linear actuator can typically be driven at 5V DC, with a required drive current of approximately 0.5A. Taking the example of a iF capacitor charged to 5V, this stores 5C of charge, which corresponds to a current flow of O.5A for lOs. The capacitor will not be fully discharged, as a voltage needs to be maintained to drive the linear actuator. For example, if the linear actuator is operated for is and draws a constant current of O.5A, 4.5C charge will remain on the capacitor, and the voltage will only have dropped to 4.5V (ignoring the effect of the capacitor being connected to the phone line).

It can be seen that when the linear actuator is simply to provide infrequent switching between two states, it is perfectly practical to operate this using the charge stored in the capacitor.

To charge the capacitor from 4.5C (i.e. O.5C of charge), even with a low off-hook current of 2OmA takes 25s. Thus, the capacitor can be recharged after use by a short period (of the order of a minute) of off-hook current draw from the telephone line. For emergency applications, the initial operation of the valve is the critical step to prevent damage or flooding, and the subsequent operation of the valve is less critical, and is likely to be in the presence of engineers at the site in any case. Thus, the recharge time is not critical in many applications, because a once-only operation is required to provide the required safety function.

The capacitor may also be charged by the on-hook current, of course over a longer period of time.

The power and linear actuator controller 18 receives a charge input 19 in the form of the phone line both for charging capacitor 17 in the off-hook position and for trickle charging in the on-hook position to compensate for leakage current of the capacitor. The controller provides the power to the capacitor from power line 19, and typically has voltage conversion capability to convert between the phone line voltage and the required drive voltage for the linear actuator.

The power and linear actuator controller also controls the operation of the linear actuator based on a control signal(s) that is decoded from the phone line 19 by telephone line interface and communication controller 20.

The power and linear actuator controller ensures that the current drawn from the phone line 19 does not exceed the permitted levels in the on-hook and off-hook modes.

In a preferred implementation, the telephone line interface and communication controller 20 analyses and terminates a telephone line, and decodes external commands received in DTMF code, including by means of pre-recorded messages It then checks and confirms executions of commands by the linear actuator 11. The power and actuator controller 18 ensures optimal charging and discharging of the power storage capacitor, including trickle charging the capacitor in an on-hook position. The controller 18 provides sequences of power signals for driving of the linear actuator and analyses the position of the actuator shaft Capacitors with the required high capacitance are widely available, for example from the company Epcos (Trade Mark). Typically, the capacitors have activated carbon electrodes, and an electrode separator soaked in electrolyte. By selecting a capacitor with a leakage current of less than 2OpA, the on-hook current limits are not exceeded.

Different countries impose different limitations on equipment connected to the phone lines, and the capacitor and linear actuator will be chosen so that the capacitor can remain charged using a trickle charge corresponding to an allowed on-hook current. The capacitor is selected to store sufficient charge to enable operation of the linear actuator, based on the current drawn and time of operation.

As charge is removed from the capacitor, the voltage will drop, and the capacitance is chosen so that the capacitor only discharges to a level that still provides correct operation voltage for the linear actuator.

The capacitor may be much larger, for example with a capacitance of more than 5F. lndeed capacitors up to thousands of Farads are available, and the higher the capacitance, the more stable the linear actuator drive voltage, but with longer initial charge time, and higher leakage currents.

Apart of the suggested hybrid linear actuator, many different types of linear actuator are widely available, and the linear actuator can be selected based on the operating voltage, current and mechanical thrust which can be provided. In many applications, the linear actuator only needs to toggle between two states and simple and reliable devices are widely available for this purpose.

*Figure 4 shows another application of the electro-mechanical actuator of the invention, for controlling a pressure regulating valve 21, which is included in a standard pressure control loop with a main hydraulic valve by paths 22 and 23.

The regulating valve 21 allow remote control of a pressure at the valve outlet.

Thus, the invention can be used for analogue control of an external device as well as for discrete control as previously described.

One preferred application of the invention has been described, using telephone lines for control and powering of the remote devices. There are many locations where connection to a phone line is much easier than connection to mains electricity, and this invention will be of particular interest in these applications. However, the invention more generally provides an actuator which can be operated with a very low current supply line. The remote actuator can for example be powered by a solar panel (in combination with a rechargeable battery). The battery does not need to have the capability of driving the actuator.

Again, its function can simply be to provide the capacitor leakage current during the night, The solar panel provides the capacitor leakage current and the battery trickle charge during the day. Thus, in this example, the battery also can have an output current not sufficient to drive the linear actuator.

The control signal can then be provided by using a mobile phone network, with the remote devices having a cellular telephone receiver.

The actuator can be provided as a retro fit device to an existing hydraulic valve, such as shown in Figure 1, as it replaces only the control valve. This replacement can be done in service with the valve open.

There are other example of actuator for which the same issues arise, and where mains power is not available. An example is door lock actuators.

Various modifications will be apparent to those skilled in the art. ELECTRO-MECHANICAL ACTUATOR

This invention relates to electro-mechanical actuators, and particularly to remotely controlled actuators.

There are many examples of electro-mechanical actuator where it is desirable to have the ability to control the device remotely. One example is water valves, which are used to isolate sections of the water mains supply system, to allow repairs or replacement to be carried out. In the event of a failure or damage to a water mains pipe, it is desirable to isolate the fault as quickly as possible. Of course, the water supply system extends to many remote areas, and it has been recognised that the ability to control the gate valves remotely is desirable.

It is known to provide telephone-based control commands to remote devices, using a telephone modem to interpret control commands. The use of the internet and/or mobile phones for controlling remote devices is also now widespread, and this has the advantage that control signals can be provided wirelessly.

A problem with the remote control of electrical devices is that a power supply is nevertheless needed to drive the device. For devices in remote applications, where remote control is particularly desirable, there is often no mains electrical supply.

According to the invention, there is provided a remotely controlled electro-mechanical actuator, comprising: a linear actuator for providing mechanical actuation; a capacitor for storing charge for use in driving the linear actuator; a power line input; and a control circuit for controlling the operation of the linear actuator using a control signal received from a remote location, wherein the power line input is for connection to a power source with a maximum power line supply current less than the required drive current of the linear actuator, and a leakage current of the capacitor is less than the maximum power line supply current.

This use of a capacitor with a low leakage current (e.g. below 5OpA) enables the leakage current to be supplied by a phone line, so that the on-hook allowed current draw from the phone line can be used to charge the capacitor and maintain the capacitor charged. Thus, the power line input can be connected to a Public Switched Telephone Network (PSTN) or telephone line.

A high capacitance is preferred, for example of more than iF, and this enables the capacitor to provide the required short term current surge to operate the linear actuator. Preferably, the desired duty cycle with which the linear 10' actuator is driven is very low. For example, the operation of the device can be completed in the order of a second or seconds, whereas the time between successive operations will typically be at least minutes.

The high desired capacitance can be obtained using a capacitor which comprises activated carbon electrodes, and an electrode separator soaked in electrolyte. The capacitor preferably has a leakage current of less than 2OpA. This is well below the allowed 5OpA on-hook current draw for phone lines in some countries. The capacitor may have a very large capacitance of more than 5F.

The actuator may further comprise a phone line input for connection to a phone line power supply for providing a trickle capacitor charge current. This means that mains power is not required to power the device, Instead, the phone line is used to draw a trickle current to keep the capacitor charged, and the capacitor provides the short period high current pulse to operate the linear actuator.

The control circuit can control the charge flow to the capacitor from the phone line input. This enables the system to operate without exceeding the allowed phone line currents.

The control circuit can be operable in two modes: a first, trickle charge mode, in which a current of less than a maximum phone line on-hook permissible current (e.g. 5OpA in the UK)' is provided both to keep electronic control circuit in a "waiting mode" ready to accept control signal from PSTN and compensate a leakage current of the capacitor; and a second, recharge mode, in which a current of less than a maximum phone line off-hook current (e.g. lOOmA) is provided from the phone line input to charge the capacitor.

The recharge mode is initiated during an active call. This active call is then used to aHow a larger current to be used to charge the capacitor more quickly, if required. The call also enables the required control commands to be provided to the control circuit in a double-tone multifrequency mode (DTMF).

The linear actuator can control a valve, for example a pilot/control valve of a hydraulic valve.

The invention also provides a hydraulic valve, comprising: a valve disc provided in the fluid path between a fluid inlet and outlet; a valve disc control chamber, wherein the pressure in the valve lever control chamber controls the open or closed position of the valve; a first fluid connection between the fluid inlet and the control chamber; and an actuator of the present invention for selectively coupling the control chamber to the first fluid connection.

In this invention, the linear actuator can also control a pressure regulator which can be connected in a pressure regulating loop of a known hydraulic pressure control valve, for example for pressure reduction.

The invention also provides a method of remotely controlling an electro-mechanical actuator, comprising: supplying power to the actuator from a telephone line having a maximum power supply current less than the required drive current of the actuator; charging a capacitor using the telephone line power supply; providing a control signal over the telephone line; operating the actuator using charge stored in the capacitor in response to the control signal; and recharging the capacitor using the telephone line power supply.

An example of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a known hydraulic control valve; Figure 2 shows schematically the electrical layout of an actuator of the invention; Figure 3 shows schematically the mechanical layout of a 3-way pilotlcontrol valve, driven by a linear actuator, which can be used as the control valve in the valve of Figure 1; and Figure 4 shows an alternative use of the actuator of the invention.

The invention provides a remotely controlled electro-mechanical actuator, in which a capacitor stores charge for use in driving a linear actuator for providing mechanical actuation for driving an external device. The power line input is for connection to a power source with a maximum power line supply current less than the required drive current of the linear actuator, and a leakage current of the capacitor is less than the maximum power line supply current.

In a preferred arrangement, the actuator comprises a telephone line interface and communication controller, a power and liner actuator controller and a linear actuator The actuator can thus be powered by a phone line, as result of a large capacitance of the implemented capacitor with a low leakage current.

One application of particular interest is for the remote control of water control valves, for example used in the mains water system. For this reason, the operation of a typical hydraulic control valve used in that application will first be described with reference to Figure 1.

The hydraulic valve comprises a fluid inlet 1 and a fluid outlet 2. A valve seal disc 3 is provided in the fluid path between the fluid inlet and the fluid outlet and can close the fluid inlet as shown in Figure 1. A valve seal disc control chamber 4 is used to control the open or closed position of the valve seal disc 3.

The pressure in the chamber 4 acts against a diaphragm 5 which is connected to the valve seal disc 3 by a rod 6. When the pressure in the control chamber 4 is equal to the inlet pressure, the valve is closed, as a result of differential areas, i.e. the control chamber pressure acts on a larger area than the area of the seal disc exposed to the inlet fluid flow. Thus, the valve can be closed by providing a fluid connection between the chamber 4 and the inlet 1, for example as shown by connecting pipes 7 and 8.

To open the valve, the pressure in the chamber 4 is reduced. This can be by venting the chamber to air, or by connecting it to a different area with a low pressure, for example the outlet side of the valve by pipes 8 and 9.

A small pilot/control valve 10 can be used for controlling the overall valve operation by controlling the coupling of the pipe 8 to pipe 7 or 9.. This control valve is not exposed to the fluid flow rates or volumes of the main valve and can therefore be a reliable low cost device. It can be mechanically operated and/or electrically operated.

This invention relates to remotely controlled actuators, such as low current valves to perform the pilot/control valve function.

Figure 2 shows schematically the electrical layout of an actuator of the invention, which can be used as the control valve 10 in the hydraulic valve of Figure 1. Figure 3 shows the mechanical layout. As shown, the arrangement has three inputs/outputs, with a valve lever in the path between two of the inputs/outputs, to selectively block one of them.

The actuator of the invention comprises a linear actuator 11 for providing mechanical actuation. This provides the desired mechanical movement to operate the pilot/control valve 10. The linear actuator provides linear reciprocation of an output shaft, and this can be used to move a closing lever of the valve between two positions. This is shown schematically in Figure 3, in which the reciprocating shaft is shown as 12, and which drives a valve seal lever 13 between two positions, to selectively close one of two passages 14 or 15. In this way, an inlet passage 16 is selectively coupled to one or other of the passages 14 or 15. In this example, the inlet passage 16 can be connected to the control chamber 4, and the other passages 14 and 15 can be connected to the inlet 1 and outlet 2 of the hydraulic valve, Fig.1.

A capacitor(s) 17 (Fig.2) stores charge for use in driving the linear actuator 11 and typically has a leakage current of less than 5OpA and a capacitance of more than iF.

This use of a capacitor with a leakage current below 5OpA enables the leakage current to be supplied by a phone line 19, so that the on-hook allowed current draw from the phone line can be used to charge the capacitor and maintain the capacitor charged. The high capacitance of more than iF enables the capacitor to provide the required short term current surge to operate the linear actuator. Preferably, the desired duty cycle with which the linear actuator is driven is very low. For example, the operation of the device can be completed in the order of a second or seconds, whereas the time between successive operations will typically be at least minutes.

A preferred example of linear actuator is a hybrid linear actuator that converts the rotary motion of a stepping motor into linear motion by the most effective way -within the stepper motor itself. This type of linear actuator features precision, reliability and unmatched performance-to-size ratios, for example from the company Haydon Switch and Instruments, Inc. The most important features of a hybrid linear actuator is its very high thrust and ability to maintain the same position of its shaft after de-energising of the actuator withstanding considerable forces that can be applied to the shaft.

Known hybrid linear actuator can typically be driven at 5V DC, with a required drive current of approximately 0.5A. Taking the example of a iF capacitor charged to 5V, this stores 5C of charge, which corresponds to a current flow of O.5A for lOs. The capacitor will not be fully discharged, as a voltage needs to be maintained to drive the linear actuator. For example, if the linear actuator is operated for is and draws a constant current of O.5A, 4.5C charge will remain on the capacitor, and the voltage will only have dropped to 4.5V (ignoring the effect of the capacitor being connected to the phone line).

It can be seen that when the linear actuator is simply to provide infrequent switching between two states, it is perfectly practical to operate this using the charge stored in the capacitor.

To charge the capacitor from 4.5C (i.e. O.5C of charge), even with a low off-hook current of 2OmA takes 25s. Thus, the capacitor can be recharged after use by a short period (of the order of a minute) of off-hook current draw from the telephone line. For emergency applications, the initial operation of the valve is the critical step to prevent damage or flooding, and the subsequent operation of the valve is less critical, and is likely to be in the presence of engineers at the site in any case. Thus, the recharge time is not critical in many applications, because a once-only operation is required to provide the required safety function.

The capacitor may also be charged by the on-hook current, of course over a longer period of time.

The power and linear actuator controller 18 receives a charge input 19 in the form of the phone line both for charging capacitor 17 in the off-hook position and for trickle charging in the on-hook position to compensate for leakage current of the capacitor. The controller provides the power to the capacitor from power line 19, and typically has voltage conversion capability to convert between the phone line voltage and the required drive voltage for the linear actuator.

The power and linear actuator controller also controls the operation of the linear actuator based on a control signal(s) that is decoded from the phone line 19 by telephone line interface and communication controller 20.

The power and linear actuator controller ensures that the current drawn from the phone line 19 does not exceed the permitted levels in the on-hook and off-hook modes.

In a preferred implementation, the telephone line interface and communication controller 20 analyses and terminates a telephone line, and decodes external commands received in DTMF code, including by means of pre-recorded messages It then checks and confirms executions of commands by the linear actuator 11. The power and actuator controller 18 ensures optimal charging and discharging of the power storage capacitor, including trickle charging the capacitor in an on-hook position. The controller 18 provides sequences of power signals for driving of the linear actuator and analyses the position of the actuator shaft Capacitors with the required high capacitance are widely available, for example from the company Epcos (Trade Mark). Typically, the capacitors have activated carbon electrodes, and an electrode separator soaked in electrolyte. By selecting a capacitor with a leakage current of less than 2OpA, the on-hook current limits are not exceeded.

Different countries impose different limitations on equipment connected to the phone lines, and the capacitor and linear actuator will be chosen so that the capacitor can remain charged using a trickle charge corresponding to an allowed on-hook current. The capacitor is selected to store sufficient charge to enable operation of the linear actuator, based on the current drawn and time of operation.

As charge is removed from the capacitor, the voltage will drop, and the capacitance is chosen so that the capacitor only discharges to a level that still provides correct operation voltage for the linear actuator.

The capacitor may be much larger, for example with a capacitance of more than 5F. lndeed capacitors up to thousands of Farads are available, and the higher the capacitance, the more stable the linear actuator drive voltage, but with longer initial charge time, and higher leakage currents.

Apart of the suggested hybrid linear actuator, many different types of linear actuator are widely available, and the linear actuator can be selected based on the operating voltage, current and mechanical thrust which can be provided. In many applications, the linear actuator only needs to toggle between two states and simple and reliable devices are widely available for this purpose.

*Figure 4 shows another application of the electro-mechanical actuator of the invention, for controlling a pressure regulating valve 21, which is included in a standard pressure control loop with a main hydraulic valve by paths 22 and 23.

The regulating valve 21 allow remote control of a pressure at the valve outlet.

Thus, the invention can be used for analogue control of an external device as well as for discrete control as previously described.

One preferred application of the invention has been described, using telephone lines for control and powering of the remote devices. There are many locations where connection to a phone line is much easier than connection to mains electricity, and this invention will be of particular interest in these applications. However, the invention more generally provides an actuator which can be operated with a very low current supply line. The remote actuator can for example be powered by a solar panel (in combination with a rechargeable battery). The battery does not need to have the capability of driving the actuator.

Again, its function can simply be to provide the capacitor leakage current during the night, The solar panel provides the capacitor leakage current and the battery trickle charge during the day. Thus, in this example, the battery also can have an output current not sufficient to drive the linear actuator.

The control signal can then be provided by using a mobile phone network, with the remote devices having a cellular telephone receiver.

The actuator can be provided as a retro fit device to an existing hydraulic valve, such as shown in Figure 1, as it replaces only the control valve. This replacement can be done in service with the valve open.

There are other example of actuator for which the same issues arise, and where mains power is not available. An example is door lock actuators.

Various modifications will be apparent to those skilled in the art.

Claims (14)

1. A remotely controlled electro-mechanical actuator, comprising: a linear actuator for providing mechanical actuation; a capacitor for storing charge for use in driving the linear actuator; a power line input; and a control circuit for controlling the operation of the linear actuator using a control signal received from a remote location, wherein the power line input is for connection to a power source with a maximum power line supply current less than the required drive current of the linear actuator, and a leakage current of the capacitor is less than the maximum power line supply current.

2. An actuator as claimed in claim 1, wherein the capacitor has a leakage current of less than 5OpA and a capacitance of more than IF.

3. An actuator as claimed in claim I or 2, wherein the capacitor comprises activated carbon electrodes, and an electrode separator soaked in electrolyte.

4. An actuator as claimed in any preceding claim, wherein the capacitor has a leakage current of less than 5OpA.

5. An actuator as claimed in any preceding claim, wherein the capacitor has a capacitance of more than 1 F, more preferably more than 5F.

6. An actuator as claimed in any preceding claim, wherein the linear actuator comprises a hybrid linear actuator that converts the rotary motion of a stepping motor into linear motion.

7. An actuator as claimed in any preceding claim, wherein the power line input comprises a phone line input for connection to a phone line.

I

8. An actuator as claimed in claim 7, wherein the control circuit controls the charge flow to the capacitor from the phone line input.

9. An actuator as claimed in claim 9, wherein the control circuit is operable in two modes: a first, trickle charge mode, in which a current of less than a maximum phone line on-hook current is provided to the capacitor; and a second, recharge mode, in which a current of less than a maximum phone line off-hook current is provided from the phone line input to charge the capacitor.

10. An actuator as claimed in any preceding claim, comprising a valve.

11. An actuator as claimed in claim 10, comprising a control valve of a hydraulic valve.

12. A hydraulic valve, comprising: a fluid inlet; a fluid outlet; a valve disc provided in the fluid path between the fluid inlet and the fluid outlet; a valve disc control chamber, wherein the pressure in the valve disc control chamber controls the open or closed position of the valve; a first fluid connection between the fluid inlet and the control chamber; and an actuator as claimed in claim 11 for selectively coupling the control chamber to the first fluid connection.

13. A valve as claimed in claim 12, further comprising a second fluid connection between the fluid outlet and the control chamber; and wherein the actuator is for selectively coupling the control chamber to the first or second fluid connections.

14. A method of remotely controlling an electro-mechanical actuator, comprising: supplying power to the actuator from a telephone line having a maximum power supply current less than the required drive current of the actuator; charging a capacitor using the telephone line power supply; providing a control signal over the telephone line; operating the actuator using charge stored in the capacitor in response to the control signal; and recharging the capacitor using the telephone line power supply.

14. A method of remotely controlling an electro-mechanical actuator, comprising: supplying power to the actuator from a telephone line having a maximum power supply current less than the required drive current of the actuator; charging a capacitor using the telephone line power supply; providing a control signal over the telephone line; operating the actuator using charge stored in the capacitor in response to the control signal; and recharging the capacitor using the telephone line power supply.

1. A remotely controlled electro-mechanical actuator, comprising: a linear actuator for providing mechanical actuation; a capacitor for storing charge for use in driving the linear actuator; a power line input; and a control circuit for controlling the operation of the linear actuator using a control signal received from a remote location, wherein the power line input is for connection to a power source with a maximum power line supply current less than the required drive current of the linear actuator, and a leakage current of the capacitor is less than the maximum power line supply current.

2. An actuator as claimed in claim 1, wherein the capacitor has a leakage current of less than 5OpA and a capacitance of more than IF.

3. An actuator as claimed in claim I or 2, wherein the capacitor comprises activated carbon electrodes, and an electrode separator soaked in electrolyte.

4. An actuator as claimed in any preceding claim, wherein the capacitor has a leakage current of less than 5OpA.

5. An actuator as claimed in any preceding claim, wherein the capacitor has a capacitance of more than 1 F, more preferably more than 5F.

6. An actuator as claimed in any preceding claim, wherein the linear actuator comprises a hybrid linear actuator that converts the rotary motion of a stepping motor into linear motion.

7. An actuator as claimed in any preceding claim, wherein the power line input comprises a phone line input for connection to a phone line.

I

8. An actuator as claimed in claim 7, wherein the control circuit controls the charge flow to the capacitor from the phone line input.

9. An actuator as claimed in claim 9, wherein the control circuit is operable in two modes: a first, trickle charge mode, in which a current of less than a maximum phone line on-hook current is provided to the capacitor; and a second, recharge mode, in which a current of less than a maximum phone line off-hook current is provided from the phone line input to charge the capacitor.

10. An actuator as claimed in any preceding claim, comprising a valve.

11. An actuator as claimed in claim 10, comprising a control valve of a hydraulic valve.

12. A hydraulic valve, comprising: a fluid inlet; a fluid outlet; a valve disc provided in the fluid path between the fluid inlet and the fluid outlet; a valve disc control chamber, wherein the pressure in the valve disc control chamber controls the open or closed position of the valve; a first fluid connection between the fluid inlet and the control chamber; and an actuator as claimed in claim 11 for selectively coupling the control chamber to the first fluid connection.

13. A valve as claimed in claim 12, further comprising a second fluid connection between the fluid outlet and the control chamber; and wherein the actuator is for selectively coupling the control chamber to the first or second fluid connections.